The present invention relates to a video signal processing apparatus and a video displaying apparatus suitable for processing and displaying video signals of several format types.
Video displaying apparatus such as TV sets have given a demand for displaying video signals of several format types with the start of digital TV broadcasting.
Format types for video signals are interlaced video (480i) of 525 total scanning lines and 480 effective scanning lines, interlaced video (1080i) of 1125 total scanning lines and 1080 effective scanning lines, progressive video (480p) of 525 total scanning lines and 480 effective scanning lines, and progressive video (720p) of 750 total scanning lines and 720 effective scanning lines.
These format types have the same vertical frequency. The number of effective scanning lines per field is however different, i.e., 480/2 lines for 480i, 1080/2 lines for 1080i, 480 lines for 480p, and 720 lines for 720p. The horizontal frequency is also different, i.e., 15.75 KHz for 480i, 33.75 KHz for 1080i, 31.5 KHz for 480p, and 45 KHz for 720p.
It has been studied to switch the horizontal frequency over 15.75 KHz, 33.75 KHz, 31.5 KHz and 45 KHz for video displaying apparatus in displaying video signals of all of these format types. Video displaying apparatus have to be compatible with these four different horizontal frequencies.
Interlace-to-progressive (I-P) conversion of 480i-video signals to 480p-video signals results in three different horizontal frequencies. Video displaying apparatus still have to be compatible with these three different horizontal frequencies.
To lighten a burden for video displaying apparatus, it has been studied to standardize several video formats into 1080i only.
For example, video displaying apparatus equipped with a cathode ray tube (CRT) require CRT-synchronization adjustments per format for displaying video signals of different formats, which causes large change in deflector voltage, thus a heavy burden for deflectors. Other types of video displaying apparatus also have to bear a heavy burden for displaying video signals of different formats.
CRT-synchronization adjustments per format requires temporal video-masking (blanking) on screen for picture quality. This results in complex control operation to video displaying apparatus and also no videos on screen temporarily. Accordingly, displaying video signals of different formats causes several problems.
For solving such problems, several video formats may be standardized into 1080i only as mentioned above. However, this also causes a problem. In detail, conversion of 480i into 1080i will produce scanning lines 9/4 times the number of original scanning lines. Moreover, conversion of 720p into 1080i will produce scanning lines 3/4 times the number of original scanning lines.
Standardization of video formats into 1080i thus results in the number of scanning lines made larger and also smaller through format conversion. This requires large hardware for interpolation filters used for format converting circuitry.